obama were seen boarding air force one and on board a kind of presidential car pool. former first lady, secretary hillary clinton and laura bush and former president george w. bush. on board the group sharing memories of mandela as all eyes turned toward johannesburg and the service now just hours away. abc's chief foreign correspondent terry moran is there. >> reporter: doves released into the skies outside nelson mandela's home today, a fitting tribute for a great man of peace. in johannesburg, meanwhile, it was all business. workers prepping the fnb stadium, capacity 94,000, for the massive memorial service taking place here tomorrow. security preparations are intense, and with good reason. the world has never seen a gathering of leaders like this one. flying in from more than 90 countries, from argentina to pakistan, trinidad to china, including four u.s. presidents, obama, who has been chosen to speak tomorrow and three of his predecessors which has the american ambassador here scrambling. >> the president went wheels up about an hour and a half ago. so, they're